• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.5
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• pp.286-291
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• 2014

In this study, novel ultrasonic rotary motor of hexadecagon shape stator was proposed. Stator of the hexadecagon ultrasonic motor was composed of an elastic ring and ceramics. The elastic ring had sixteen sides and sixteen angular points. Eight ceramics were attached on the outer surface of the eight sides of the ring. When rotor of cylindrical shaft was inserted inside of the ring stator, central lines of the sixteen sides of the stator hold the shaft by the slight pressures(frictions). This slight pressure was a preload of the motor and it could be controlled by radius and thickness of the ring. When two sinusoidal voltages which have 90 degree phase difference were applied to each four ceramics, elliptical displacements of inner surface of the ring were obtained. These elliptical displacements of the inner surface rotated the shaft rotor through the frictions. The proposed hexadecagon ultrasonic motor was designed and analyzed by using the finite element method (FEM), depending on materials of the elastic ring. Based on the FEM results, one model of motor which showed maximum displacement at contact points was chosen and fabricated. And characteristics of the motor were compared with simulated results. When the motor was fabricated with these results, EL20ET0.5CT0.5CW2 model showed 115[rpm] speed about input voltage of 60[Vrms] at 65.6[kHz]. And the maximum torque of 6[gfcm] was obtained. From these results, the hexadecagon shaped ultrasonic motor can be used to actuator for optical device which needs detailed position control. Also it can be used to medical and portable device by reducing size and weight.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.7
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• pp.841-847
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• 2018

Since global energy consumption and demand for energy have dramatically risen, a focus on environmental problems and sustainability has become more important. Clean and renewable energy sources such as offshore wind power generation have received attention among new renewable energy options as alternative energy resources. Due to maintenance and operational perspectives, offshore wind farms have been planned for installation in many coastal waters. However, development of offshore wind farms faces interference from existing maritime traffic along the planned areas. In order to safely and effectively govern marine traffic in the vicinity of wind farms and inner areas, standard criteria are suggested to allow vessels to sail the internal waters of offshore wind farm areas. Therefore, the purpose of this study is to establish allowable criteria for sailing vessels and safety zones for offshore wind farms by investigating the local regulations of various offshore wind farm cases overseas. The commended inner safety zone of wind farms is proposed to be a distance of 150 % of the rotation diameter of the wind turbine rotor and a distance of 200 m from the outer wind turbine for the outer safety zone. Besides this, the allowable criteria for sailing vessels within a wind farm is proposed to have an air draft of 14.47 m south-west wind farm sea areas for a minimum margin to avoid hull contact through evaluation of the tide and height of a wind turbine. further studies will be needed to establish vessel sailing criteria among adjacent offshore wind farms as well as vessel sailing criteria within a single offshore wind farm.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.9
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• pp.943-954
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• 2010

In this study, a radial inflow type turbine was applied and the outer diameter of the turbine rotor was 108 mm. The turbine blade on a circular plate disc was designed as an axial-type because its partial admission rate was 1.4-4.1%. The turbine consisted of three stages. The performance test has been conducted with various admission rates, tip clearances and nozzle flow angles. The turbine output power was measured on each stage. The turbine performance was obtained in a wide rotational speed range in order to compare its performance according to various operating conditions. The net specific output torque was also measured to compare its overall performance. Computational analysis was conducted for predicting turbine performance. The computed results were in good agreement with the experimental results.

• International Journal of Automotive Technology
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• v.8 no.6
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• pp.799-806
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• 2007

One method for improving the torque capacity of the CVT is to use a split-powered CVT(SPCVT) to reduce the power transmitted into a continuously variable unit(CVU). A variable bridge SPCVT with two planetary gear units(PGUs), which are composed of a sun gear, a ring gear, and carrier and planetary gears, can minimize the power to the CVU. However, a SPCVT with a conventional CVT should possess a dual mode, which would allow the conventional CVT to be used at high speeds and an additional gear train to be used at low speeds. The inner-spherical CVU(ISCVU) with an inner and outer spherical contact mechanism developed in this study can cover the range from low to high speeds. The rated power and the overall speed ratios were 100 kW and $0.09{\sim}0.36$, respectively. Power efficiency was numerically calculated to be over 90% over the speed ratio range of $0.1{\sim}0.29$. The maximum shear stress at the two contact areas of the rotor pairs, the minimum life and the overall size were estimated to be 700 MPa, 276 kh and $350{\times}350{\times}400mm^3$, respectively. This study shows that an ISCVU and a variable bridge type PGU can realize the SPCVT with a single mode for a vehicle.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.9
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• pp.67-77
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• 2010

An internal lobe pump is suitable for oil hydraulics of machine tools, automotive engines, compressors, constructions and other various applications. In particular, the pump is an essential machine element of an automotive engine to feed lubricant oil. The subject of this paper is the theoretical analysis of internal lobe pump whose the main components are the rotors: usually the outer one is characterized by lobe with elliptical and involute shapes, while the inner rotor profile is determined as conjugate to the other. And the integrated design system which is composed of three main modules has been developed through AutoLISP under AutoCAD circumstance plus CFD-ACE+. It generates new lobe profile and calculates automatically the flow rate and flow rate irregularity according to the lobe profile generated. CFD simulation results show trends similar to those carried out in experiments, and a quantitative comparison is presented. Results obtained from the automotive integrated design system enable the designer and manufacturer of oil pump to be more efficient in this field.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.465-465
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• 2009

Wind power is one of the most reliable renewable energy sources and the installed wind turbine capacities are increasing radically every year. Although wind power has been favored by the public in general, the problem with the impact of wind turbine noise on people living in the vicinity of the turbines has been increased. Low noise wind turbine design is becoming more important as noise is spreading more adverse effect of wind turbine to public. This paper demonstrates the design of 10 kW class wind turbines, each of three blades, a rotor diameter 6.4m, a rated rotating speed 200 rpm and a rated wind speed 10 m/s. The optimized airfoil is dedicated for the 75% spanwise position because the dominant source of a wind turbine blade has been known as trailing edge noise from the outer 25% of the blade. Numerical computations are performed for incompressible flow and for Mach number at 0.145 and for Reynolds numbers at $1.02{\times}10^6$ with a lift performance, which is resistant to surface contamination and turbulence intensity. The objective in the low design process is to reduce noise emission, while sustaining high aerodynamic efficiency. Dominant broadband noise sources are predicted by semi-empirical formulas composed of the groundwork by Brooks et al. and Lowson associated with typical wind turbine operation conditions. During the airfoil redesign process, the aerodynamic performance is analyzed to minimize the wind turbine power loss. The results obtained from the design process show that the design method is capable of designing airfoils with reduced noise using a commercial 10 kW class wind turbine blade airfoil as a basis. The new optimized airfoil clearly indicates reduction of total SPL about 3 dB and higher aerodynamic performance.

• Tribology and Lubricants
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• v.34 no.1
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• pp.33-41
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• 2018

This paper describes a new test rig for identification of rotordynamic force coefficients of squeeze film dampers (SFDs) in automotive turbochargers (TCs). Prior studies have mainly concentrated on relatively large-sized SFDs used in aircraft engines, turbocompressors, and turbopumps. The main objective of the current study is to propose a test rig for identification of dynamic force coefficients of small-sized SFDs (a journal diameter of ~11 mm). The current test rig consists of a journal, a SFD cartridge, four support rods, an upper structure, a data acquisition (DAQ) system, and an oil circulation unit. The annular gaps between the journal outer surface and SFD cartridge inner surface create SFD film lands. The damper has two parallel film lands separated by a central groove, having an axial length and depth of 3 mm. Each film land has a length of 4 mm with a $40{\mu}m$ radial clearance. The static load and dynamic impact tests identify the structural characteristics (i.e., stiffness and natural frequency) of the journal and assembled test rig. The measurements show good agreement with predictions. The SFD performance data from this test rig will be used to develop innovative TC rotor systems with improved NVH and reliability characteristics incorporating advanced SFD technology.